1. Field of the Invention
The present invention relates to an obstacle detector for a vehicle, and more particularly to an apparatus for detecting an obstacle which is present in the path of a traveling vehicle, by emitting light and detecting the light reflected by the obstacle.
2. Description of the Prior Art
In the past, obstacle detectors have been proposed which radiate ultrahigh frequency electromagnetic waves in the microwave or millimeter wavelength range, and detect the waves reflected by an obstacle present in the path of the vehicle, thereby detecting the obstacle. Such detectors, however, have the following disadvantages due to use of the ultrahigh frequency waves:
(1) The costs of components for ultrahigh frequency use are high compared with those of components for use at lower radio frequencies. Therefore, a detector for such ultra high frequency use is relatively expensive.
(2) When a transmitting and receiving antenna is designed so that its power half-width at a frequency of 35 GHz is .+-.2.degree., the minimum size of the antenna is about 150 millimeters. Thus the mounting of the antenna on a vehicle presents space problems.
(3) The wave length of such ultrahigh frequency is relatively long, for example about 1 cm (30 GHz) at a minimum. Thus although the directivity of the antenna is sharp, the limit of the detection area is unclear. An obstacle of high reflectivity, in the vicinity of the detection area, may be falsely detected.
The present invention intends to eliminate these defects and problems.